Harmonic reject receiver architecture and mixer

ABSTRACT

Receiver architectures and methods of processing harmonic rich input signals employing harmonic suppression mixers are disclosed herein. The disclosed receivers, mixers, and methods enable a receiver to achieve the advantages of switching mixers while greatly reducing the mixer response to the undesired harmonics. A harmonic mixer can include a plurality of mixers coupled to an input signal. A plurality of phases of a local oscillator signal can be generated from a single local oscillator output. Each of the phases can be used to drive an input of one of the mixers. The mixer outputs can be combined to generate a frequency converted output that has harmonic rejection.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/432,666, filed Apr. 29, 2009, which is a divisional of U.S.application Ser. No. 11/302,531, filed Dec. 12, 2005, which claims thebenefit of U.S. Provisional Application No. 60/635,030, filed Dec. 10,2004. The above-referenced U.S. patent applications are all is herebyincorporated herein by reference in their entirety.

BACKGROUND

The disclosure relates to electronic signal processing. Moreparticularly, the disclosure relates to a harmonic reject RF receiver,harmonic reject receiver architecture, and harmonic reject mixers.

RF communication systems often provide numerous frequency divisionmultiplexed channels distributed over a predetermined operating band. Areceiver can typically be configured to tune to a desired channel toreceive the information provided on that channel.

In many communication systems, the operating band is a relatively narrowband. That is, the operating band typically does not occupy greater thanan octave. However, in some communication systems, such as television,the operating frequency band may include hundreds of channels occupyingseveral octaves.

Such a wide operating bandwidth can present particular problems notexperienced in other systems having sub-octave operating frequencybands. For example, a wide operating bandwidth may include multiple inband interferers. The undesired channels in a television operating bandcan appear as interferers to the desired channel. The undesired channelscan be at substantially the same power level, or even at a greater powerlevel, than the power level of the desired channel.

A receiver typically filters or otherwise attenuates undesired channelsand other interference sources. However, some interferers may contributeto in band interference due to operation of the receiver, such thatfiltering is ineffective. In particular, a receiver may unintentionallyfrequency convert the harmonics of the desired input signal to the samefrequency band that is converts the desired signal.

Because the interferer can frequency convert to an in band interferencesignal, it is not possible to filter out the interference. Additionally,the input operating frequency band may span multiple octaves and mayinclude the harmonics. The receiver may not be able to sufficientlyeliminate the effects of the harmonic interferers by filtering the inputsignal.

BRIEF SUMMARY

Receiver architectures and methods of processing harmonic rich inputsignals employing harmonic suppression mixers are disclosed herein. Thedisclosed receivers, mixers, and methods enable a receiver to achievethe advantages of switching mixers while greatly reducing the mixerresponse to the undesired harmonics. A harmonic mixer can include aplurality of mixers coupled to an input signal. A plurality of phases ofa local oscillator signal can be generated from a single localoscillator output. Each of the phases can be used to drive an input ofone of the mixers. The mixer outputs can be combined to generate afrequency converted output that has harmonic rejection.

Aspects of the invention include a harmonic reject mixer that includes aplurality of mixers, each mixer having an input coupled to a common RFinput, a phase shifter having an input coupled to a common LO input anda plurality of phase shifted outputs, each of the outputs coupled to aLO input on a corresponding mixer, and a combiner having a plurality ofinputs, each input coupled to an output from an associated mixer, andconfigured to provide a combined output.

Aspects of the invention include a method of harmonic rejection mixing.The method includes generating a plurality of phases of a LO signal,mixing an input signal with each of the plurality of phases of the LOsignal to generate a plurality of mixed output signals, and combiningthe plurality of mixed output signals to provide a mixer output.

Aspects of the invention include a quadrature mixer that includes aplurality of harmonic reject mixers, each mixer having an input coupledto one of a plurality of phases of an input signal, and each mixerhaving an input coupled to a phase shifted LO, a first combiner havinginputs coupled to outputs from a first subset of the plurality ofharmonic reject mixers, and an output configured to provide a quadratureoutput, and a second combiner having inputs coupled to outputs from asecond subset of the plurality of harmonic reject mixers, and an outputconfigured to provide an in-phase output.

Aspects of the invention include a receiver that includes a filterhaving an input coupled to an RF input, and a filtered output, and aharmonic reject down converter having an input coupled to the filteredoutput, a Local Oscillator (LO) input configured to receive an LOsignal, a quadrature output, and an in-phase output.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of embodiments of the disclosurewill become more apparent from the detailed description set forth belowwhen taken in conjunction with the drawings, in which like elements bearlike reference numerals.

FIG. 1 is a simplified functional block diagram of an embodiment of areceiver in a system.

FIG. 2 is simplified functional block diagram of an embodiment of areceiver.

FIG. 3 is a simplified functional block diagram of an embodiment of areceiver front end.

FIG. 4 is a simplified functional block diagram of an embodiment of aharmonic reject mixer.

FIG. 5 is a simplified functional block diagram of an embodiment of aharmonic reject mixer.

FIG. 6 is a simplified functional block diagram of a downconverterhaving harmonic reject mixers.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

This disclosure describes harmonic reject mixers and receiverarchitectures which utilize harmonic reject mixers to permit anefficient implementation of a direct downconversion or low-IF receiver.The current approach to receiver design may employ switching mixerswithin the receiver front end. This permits the system to achieve lownoise and high linearity. However, these switching mixers alsoefficiently downconvert input signals at undesired harmonic multiples ofthe local oscillator frequency to the desired output frequency band. Thefrequency conversion of undesired signals poses a problem which isparticularly important for television applications where the desiredinput range is so wide that the likelihood of undesired harmonics ishigh. Receiver architectures and methods of processing harmonic richinput signals employing harmonic suppression mixers are disclosedherein. The disclosed receivers, mixers, and methods enable a receiverto achieve the advantages of switching mixers while greatly reducing themixer response to the undesired harmonics.

FIG. 1 is a simplified functional block diagram of an embodiment of areceiver 100 implementing harmonic reject signal processing in a system10. The following description describes an embodiment in which thesystem 10 is configured to operate as a television receiver. However,the system 10 can be any of a plurality of systems. For example, thesystem 10 can be a television, television receiver, set top box, ortelevision tuner integrated within a video recorder or some othertelevision receiver. In other embodiments, the system 10 can be a radioreceiver, wireless transceiver, telephone receiver, cellular telephone,cordless telephone, or some other communication device.

The system 10 can include a source switch 12 that can be coupled to oneor more signal sources. For example, a first source input can be coupledto an antenna 2 and a second source input can be coupled to a wiredsource, such as a cable coupled to a cable television distributor. Thesource switch 12 is not limited to coupling only one type of signal tothe receiver 100. For example, the source switch 12 can be coupled to atelevision signal source, for example, via the antenna 2, and can becoupled to a radio source, for example, via the cable 4.

The source switch 12 can be configured to couple any one of the signalsfrom any signal source to the input of the receiver 100. The receiver100 can be, for example, configured to selectively process televisionsignals received from a signal source, such as analog television signalsformatted according to an analog television standard, such as NTSC, PAL,SECAM, or some other analog television standard. The receiver 100 canalso be configured to process digital television signals, such asdigital DVB-T television signals, received from one of the signalsources.

The receiver 100 can receive the RF signal from the source switch 12 andcan downconvert the signal to an output IF. The output IF from thereceiver 100 can be coupled to a demodulator 50 and from the demodulator50 to a baseband processor 60. In one embodiment, the demodulator 50 canbe configured to demodulate a television signal at a predetermined IF.The demodulated television signals are communicated to a basebandprocessor 60 that can be configured, for example, to format the signalsinto video and audio signals for corresponding video and audio outputdevices (not shown).

The system 10 can also include a mode selection module 20 that can beconfigured to receive a mode selection input from an external source(not shown) that can be, for example, a user selection or user control.The mode can correspond to an operating mode of the receiver 100, andcan be used to determine a particular operating band, channel spacing,channel bandwidths, and output IF frequency.

The mode select module 20 can be coupled to a channel select module 30.The channel select module 30 can be coupled to the mode select module 20and can be configured to generate the desired local oscillator (LO)control signals. The channel select module 30 can generate the controlsignals needed to tune the LO frequencies of the receiver 100 to enablereception of the desired RF signal and generation of the desired outputIF. The channel select module 30 can also receive one or more inputsignals from an external source (not shown), such as a user interface orsome other module or device that can indicate a desired channelselection.

The channel select module 30 can independently control the RF and IF LOswithin the receiver 100. For example, the channel select module 30 cantune the RF LO to a frequency that is based on both a mode and a desiredchannel. The channel select module 30 can also be configured to controlthe frequency of the IF LO and may be configured to control the IF LObased only on the desired mode. In other embodiments, the channel selectmodule 30 can be configured to tune both the RF and LO frequencies foreach channel.

The channel select module 30 can also be configured to controlcalibration of the receiver 100. The calibration can include DC offsetcalibration and In-phase (I) and Quadrature (Q) signal balancing. Forexample, the channel select module 30 can control an RF switch withinthe receiver 100 and can initiate the DC offset calibration. In anotherembodiment, a calibration module within the receiver 100 can receive thechannel select signals and the filter control signals and can initiateDC offset calibration, including controlling the RF switch and filterbandwidths during the duration of the DC offset calibration.

A filter controller 40 can also be coupled to the mode select module 20.The filter controller 40 can be configured to provide the controlsignals to the receiver 100 that control one or more filter bandwidthswithin the receiver 100. The filter controller 40 can be configured toset the filter bandwidths based on the channel selectivity required inthe receiver 100, which can depend on the operating mode.

The filter controller 40 can also be in communication with the channelselect module 30. The filter controller 40 can be configured to controlthe filters within the receiver 100 to predetermined bandwidths for apredetermined calibration duration following each channel change. Forexample, the filter controller 40 can be configured to tune the filtersto a minimal bandwidth during DC offset calibration. Alternatively, acalibration module within the receiver 100 can be configured to controlthe filter bandwidths during the calibration duration.

A processor 72 and associated memory 74 can be included within thesystem 10 and can be configured to perform one or more functions withineach of the modules. For example, the memory 74 can include one or moreprocessor 72 usable instructions in the form of software that can, whenexecuted by the processor 72, perform some or all of the functions ofthe various modules within the system 10.

FIG. 2 is a simplified functional block diagram of an embodiment of areceiver 100 that can be implemented on one or more substrates of one ormore integrated circuits (ICs). In some embodiments, it may beadvantageous to integrate the entire receiver on a single IC. In otherembodiments, it may be advantageous to integrate a portion of thereceiver 100 in a first IC or on a first substrate and integrate theremainder of the receiver 100 on a second IC or second substrate. Thefirst and second substrates can be implemented in a single package ormay be implemented in distinct packages. For example, a signal pathwithin the receiver 100 can be implemented on a first substrate and oneor more local oscillators can be implemented on a second substrate andcouple to the first substrate through one or more interconnects.

Although the signal interconnections shown in FIG. 2 appear as singleended signal interconnects, it is generally understood that some or allof the interconnections can be implemented as differential connections.It may be advantageous to implement differential interconnections, forexample, for the purposes of noise reduction.

Portions of the receiver 100 can be implemented digitally, and can beconfigured to operate on digital representations of the signal. Thedigital processing of the signals within the receiver 100, andembodiments of receivers 100 having digital portions, are not explicitlyillustrated in the receiver 100 to allow the description to focus on thefunctionality of the various blocks and modules.

The receiver 100 can be configured to provide significant harmonicrejection. When the receiver 100 is configured to process signals over awide input signal band, such as in a television receiver application,the input frequency band may span multiple octaves. As such, the inputfrequency band may have potentially numerous signals at harmonics of thedesired input signal. One or more of the signals at the harmonics of thedesired input signal may have substantial signal strength and may evenbe stronger than the desired input signal.

The signals at the harmonics of the desired input signal can appear asinterferers. Certain harmonic frequencies can be particularlytroublesome interferers because signals at these harmonic frequenciescan frequency convert to the same frequencies as the desired inputsignal. The receiver architectures and harmonic reject mixers disclosedherein can be used to substantially reduce the effects of input signalsat harmonics of the desired input signal.

The receiver 100 can include an RF amplifier 102 that is configured toreceive a signal at the input to the receiver 100 and amplify it. The RFamplifier 102 can be configured to receive a signal, for example, froman interconnect to an antenna or wired connection, such as a singleended wireline, a differential wireline, a twisted pair, a coaxialcable, a transmission line, a waveguide, an optical receiver configuredto receive an optical signal over an optical fiber, and the like, orsome other signal medium.

The RF amplifier 102 can be configured in any of several differentembodiments or combination of embodiments, depending on the application.In one embodiment, the RF amplifier 102 can be a Low Noise Amplifier(LNA). In another embodiment, the RF amplifier 102 can be a variablegain amplifier, and the gain of the RF amplifier can be selected by oneor more control lines (not shown) to the receiver 100. In the embodimentwhere the RF amplifier 102 is a variable gain amplifier, the gain of theRF amplifier 102 can be part of a gain control loop, such as anautomatic gain control (AGC) loop (not shown). The RF amplifier 102 canbe configured as a single amplifier stage or can include multipleamplifier stages. Where multiple amplifier stages are used, theamplifier stages can include serial, parallel, or a combination ofserial and parallel amplifier configurations.

The output of the RF amplifier 102 can be coupled to a filter 104 thatcan be configured as a programmable harmonic rejection filter. Thefilter 104 can be configured, for example, as a programmable bandwidthlowpass filter, having a cutoff frequency that can be programmed toreduce undesired harmonic frequency components. As described below, theuse of a harmonic reject frequency conversion stage can substantiallyreduce the constraints on the filter 104.

The output of the filter 104 can be coupled to inputs of first andsecond frequency conversion modules, here shown as a first mixer 112 anda second mixer 114. The first and second mixers 112 and 114 are shown asmixers, but can be any type of frequency conversion device exhibitingharmonic rejection. For example, the first and second mixers 112 and 114can be double balanced mixers, double-quadrature mixers,interferometers, or some other type of frequency conversion deviceconfigured to reject the harmonics of an input signal.

The first and second mixers 112 and 114 can be configured to generatein-phase (I) and quadrature (Q) frequency converted signal components.The first mixer 112 is described as part of the in-phase signal path andthe second mixer 114 is described as part of the quadrature signal pathfor purposes of discussion.

An RF LO 120 can be configured to generate a local oscillator signal tofrequency convert the received RF signal to a baseband signal or a lowIntermediate Frequency (IF) signal. As used herein, the term basebandsignal refers to baseband signals as well as to signals that aresubstantially baseband signals. A signal is substantially a basebandsignal if the frequency conversion process to downconvert a signal isimperfect, for example, due to LO offset errors or differences at thetransmitter or receiver and errors or differences in the RF signalrelative to a specified frequency of operation. For example, an RFsignal may be different from a specified operating channel due to LOfrequency shifts at the transmitter or Doppler shifts. Typically, theerror or difference is a fraction of the baseband signal bandwidth.

A low IF signal can refer to an IF frequency that is less than twice thebaseband signal bandwidth. However, in other embodiments, low IF canrefer to less than 1.5, 2.5, 3, 4, 5, 10, or some other multiple of thebaseband signal bandwidth. Typically, a low IF signal refers to a signalthat is at a frequency sufficiently low to allow processing of thesignal without additional frequency conversions.

The receiver 100 can be configured to operate using direct conversion tobaseband in some operating modes while converting to a low IF in otheroperating modes. For example, the receiver 100 can operate in low-IFmode for analog TV applications, and substantially zero-IF for digitalapplications. Using distinct frequency conversion modes for separateoperating modes may be advantageous because the receiver 100architecture can be optimized for signal characteristics.

Analog television standards such as NTSC or PAL require less channelselection and image rejection in its low-pass filtering, but are muchmore sensitive to DC offset which typically are present in a zero-IFimplementation. This makes an analog television receiver 100 more suitedfor a low-IF implementation, which may suffer from poorer channelselectivity, but which also substantially eliminates the DC offsetproblems associated with zero-IF.

Digital TV (e.g. DVB-T) requires greater channel selection, but is lesssensitive to DC offset that may be introduced by a zero-IF architecture.This makes digital TV well-suited for a zero-IF approach, which offersbetter channel selectivity and no image rejection limitations, but mayintroduce some DC offset to the signal.

The frequency of the RF LO 120 can be programmable, and the frequencycan be programmed based in part on the frequency of the desired signal.In a direct conversion frequency conversion, the output of the RF LO 120can be substantially equal to the center frequency of a double side bandinput signal. In other embodiments, the RF LO 120 can be tuned to afrequency that is a multiple of the desired input frequency, and thefrequency divided to the desired LO frequency.

The output of the RF LO 120 can be coupled to a first phase shifter 122that can be configured to generate at least two distinct versions of aLO signal that are substantially in quadrature. Because inaccuracies inthe quadrature LO signals can contribute to undesired signal componentsin the recovered signal, it is desirable to generate accurate quadratureLO signals. In one embodiment, the first phase shifter 122 can include aphase shifted signal path and a direct signal path, where the phaseshifted signal path results in a signal that is substantially 90 degreesshifted relative to the signal from the direct signal path. In anotherembodiment, the first phase shifter 122 can include a polyphase filterthat is configured to generate the two LO signals in quadrature.

The in-phase LO signal can be coupled to an in-phase LO buffer amplifier116 that amplifies the in-phase LO signal and couples it to a LO inputport of the first mixer 112. Similarly, the quadrature LO signal can becoupled to a quadrature LO buffer amplifier 118 that amplifies thequadrature LO signal and couples it to a LO port of the second mixer114.

The output of the first mixer 112 can be an in-phase baseband signalthat is coupled to an in-phase filter 132. The in-phase filter 132 canbe programmable filter whose bandwidth can be selected based on one ormore control signals (not shown) provided to the receiver 100. Thebandwidth of the in-phase filter 132 can be selected, for example, basedon a communication standard or mode that the receiver 100 is configuredto support. Therefore, where the receiver 100 is configured to supportmultiple standards having different channel bandwidths, the bandwidth ofthe in-phase filter 132 can be selected based in part on the presentlysupported mode.

When the signal is a baseband signal or a low IF signal, the in-phasefilter 132 can be configured as a low pass filter. Alternatively, thein-phase filter 132 can be configured as a bandpass filter if the low IFsignal has sufficient bandwidth to make the use of a low pass filterundesirable.

The output of the in-phase filter 132 can be coupled to a third mixer152 configured to frequency convert the in-phase signal to a desiredoutput IF. In one embodiment, the output of the in-phase filter 132 is abaseband signal and the third mixer is configured to upconvert thein-phase baseband signal to an output IF.

The third mixer 152 can be driven by a programmable LO that is generatedin much the same manner that is used to generate the LO for the firstand second mixers 112 and 114. The IF LO 140 can be programmable toallow the output IF to be selected based in part on the mode supportedby the receiver 100. For example, the receiver 100 can be configured tofrequency convert the input signals to a predetermined IF that candepend on the manner in which the user configures the system having thereceiver 100. For example, a set top box for television signals can beconfigured to generate an output signal at a predetermined IF, such as70 MHz, or at a frequency corresponding to a television channel.

The output of the IF LO 140 can be coupled to a second phase shifter 142that is configured to generate substantially quadrature LO signals. Anin-phase LO output from the second phase shifter 142 can be coupled toan in-phase buffer amplifier 156 that amplifies the in-phase LO signaland couples it to the LO input of the third mixer 152. The output of thethird mixer 152 is an in-phase IF signal that is coupled to a firstinput of a signal combiner 160.

The quadrature signal path is configured to be substantially identicalto the in-phase signal path. The two signal paths are typicallysubstantially matched to reduce undesirable signal components that canbe generated due to I and Q mismatches.

The output of the second mixer 114 can be a baseband quadrature signalthat is coupled to an input of a quadrature filter 134. The quadraturefilter 134 can be configured as a programmable low pass filter havingprogrammable bandwidth. Typically, the configuration and bandwidths ofthe in-phase and quadrature filters 132 and 134 are the same such thatthe in-phase and quadrature signal paths remain substantially matched.

The output of the quadrature filter 134 can be coupled to an input of afourth mixer 154 that is configured to upconvert the quadrature signalto the output IF. The fourth mixer 154 is driven by an LO signal that isgenerated by the IF LO 140. The output of the IF LO 140 is coupled to asecond phase shifter 142 that generates a quadrature LO signal. Thequadrature LO signal is coupled to a quadrature buffer amplifier 158which amplifies the quadrature LO signal and couples it to an LO inputof the fourth mixer 154. The output of the fourth mixer 154 can be aquadrature IF signal. The quadrature IF signal can be coupled to asecond input of the signal combiner 160.

The signal combiner 160 can be configured to combine the in-phase andquadrature IF signals. The signal combiner 160 can be, for example, asignal summer that sums the in-phase IF signal with the quadrature IFsignal. In one embodiment, the signal combiner 160 sums the two signalswhile maintaining their phases. In another embodiment, the signalcombiner 160 can invert one of the phases and sum the two signals. Inyet another embodiment, the signal combiner 160 can generate the sum ofthe two signals and can invert the output signal.

The output of the signal combiner 160 represents the output IF signal.The output IF signal can be coupled to an output filter 170 that can be,for example, a low pass filter or bandpass filter that is configured toremove undesired signal products from the IF output signal. The outputfilter 170 can be configured as a fixed bandwidth filter or can beconfigured as a programmable bandwidth filter, where the bandwidth isdetermine, in part, based on a mode of the receiver 100.

The output of the output filter 170 can be coupled to an IF amplifier172 that can be configured to amplify the output. The IF amplifier 172can be a variable gain amplifier. The gain of the IF amplifier 172 canbe controlled using one or more control inputs (not shown) on thereceiver 100. The output of the IF amplifier 172 can be the output ofthe receiver 100.

It may be advantageous to implement the entire receiver 100 on a singleintegrated circuit, such that the processes and conditions used tomanufacture the in-phase and quadrature signal components are closelymatched, resulting in more closely matched I and Q signal paths.Additionally, it may be advantageous to implement the components on asingle IC to minimize path length distances or variations thatcontribute to mismatches. A single IC implementation can also result ina smaller receiver 100 package.

FIG. 3 is a simplified functional block diagram of a harmonic rejectreceiver front end 300 configured to downconvert a desired signal tobaseband or IF while substantially attenuating signals generated by theharmonics of the desired input signal. The receiver front end 300 can beused, for example, in the receiver embodiments shown in FIGS. 1 and 2.

The receiver front end 300 is configured to receive input signals via anantenna 301. Although the receiver front end 300 is described asreceiving signals via an antenna 310. the receiver front end 300 can beconfigured to omit the antenna 310 and can receive signals via a wiredlink (not shown).

The output of the antenna 301 is coupled to an RF amplifier 102, such asa LNA. The RF amplifier 102 can be configured to amplify substantiallythe entire input frequency band. A receiver front end 300 configured tosupport processing of television signals may need to support an inputfrequency band spanning multiple octaves.

The output of the RF amplifier 102 is coupled to a programmable harmonicreject filter 140, which can be configured as a programmable bandwidthlow pass filter. The cutoff frequency of the programmable harmonicreject filter 140 can be controlled to a frequency that is based atleast in part on the frequency of the desired input signal. In someembodiments, the cutoff frequency is programmable over a wide frequencyrange that spans multiple octaves.

Harmonic rejection is typically achieved by applying large amounts offiltering prior to mixing. In RF applications where the signal band isnarrow compared with the carrier frequency of the desired input signal,harmonic rejection is a natural byproduct of front-end filtering fromband-select filters or the antenna 301. In a broadband application,harmonic interferers constitute a significant problem, and harmonicrejection low-pass filtering needs to be programmable to allow thereceiver to receive channels across the entire band while achieving thedesired harmonic suppression. The implementation of the programmableharmonic reject filter 140 incurs a power and area penalty.Additionally, rejecting input harmonics with solely a programmableharmonic reject filter 140 may have limited effectiveness, and can alsoresults in signal path losses and associated noise degradation inperformance.

The embodiment of the receiver front end 300 illustrated in FIG. 3 usesa harmonic rejection downconverter 310 to further suppress the responseto higher harmonics of the desired fundamental. The harmonic rejectdownconverter 310 can relax the filter requirements imposed on theprogrammable harmonic reject filter 140, or can improve the harmonicreject performance by providing harmonic suppression in addition to thatprovided by the programmable harmonic reject filter 140. The harmonicrejection downconverter 310 is illustrated as a double quadrature mixerimplementing harmonic reject mixers. The particular embodiment of theharmonic rejection downconverter 310 is described in further detail inassociation with FIG. 6.

In the embodiment of the receiver front end 300 shown in FIG. 3, theoutput of the programmable harmonic reject filter 140 is coupled to aninput of the harmonic rejection downconverter 310. The harmonic rejectdownconverter 310 is configured to generate quadrature output signals.The output signals can be at baseband, a low IF, or an IF, depending onthe frequencies of the desired input signal and the LO (not shown).

An in-phase filter 132 can be configured to filter the in-phase signalcomponent and a quadrature filter 134 can be configured to filter thequadrature signal component. The outputs of the filters 132 and 134 canbe coupled to additional stages for further processing, such as thoseshown in FIG. 2.

FIG. 4 is a simplified functional block diagram of an embodiment of aharmonic reject mixer 400. The harmonic reject mixer 400 can be used,for example, in the receiver of FIG. 2 or the receiver front end of FIG.3 to provide rejection of undesired harmonics of the input signal.

The harmonic reject mixer 400 includes (2n+1) switching mixers410(0)-410(2 n). The RF input signal is coupled to an input of each ofthe switching mixers 410(0)-410(2 n). Each of the switching mixers410(0)-410(2 n) is driven by a phase offset version of a LocalOscillator (LO) 420 output signal. The number of switching mixers410(0)-410(2 n) should be greater than one to achieve harmonicrejection. Each of the switching mixers 410(0)-410(2 n) can be, forexample, a CMOS switching mixer.

The output from the LO 420 is coupled to (2n+1) phase shifters430(0)-430(2 n). The phase shifters can be distinct phase shifters ordistinct phase outputs of one or more phase shifters having multipleoutputs. Each of the phase shifters 430(0)-430(2 n) is configured toshift the phase of the LO 420 signal by a predetermined discrete phase.The LO 420 signal, phase shifted in discrete steps (φ_(n)-φ_(−n)), isused to drive the LO inputs of the switching mixers 410(0)-410(2 n).

In one embodiment, the phase shifters 430(0)-430(2 n) provide (2n+1)versions of the LO signal equally spaced about a half cycle. Forexample, the phase shifters can be configured to provide LO phasesequally spaced in the interval of −90-+90 degrees. That is, each of thephase shifters 430(0)-430(2 n) can be configured to provide a discretephase shift (in degrees) determined by the formulaφ_(n)=(n/2)×360/[2(n+1)].

Each of the outputs from the switching mixers 410(0)-410(2 n) is coupledto a corresponding amplifier 440(0)-440(2 n). The switching mixer outputsignals are scaled by their respective gains G_(n)-G_(−n). In oneembodiment, each of gains is configured to equalize the signal gainthrough each of the switching mixer amplifier paths. In anotherembodiment, all of the gains are substantially the same. In stillanother embodiment, each of the individual gains can be set to adistinct value determined based on the phase shift provided by thecorresponding phase shifter. For example, the gain of each amplifier canbe based on cos(φ_(j)).

The outputs of the amplifiers 440(0)-440(2 n) are coupled to a combiner450, here shown as a signal summer. The combiner 450 combines theamplified switching mixer outputs into a single frequency convertedoutput signal.

The harmonic rejection arises from the fact that the mixer 400approximates a linear mixer (ideal multiplication by a sinusoid) usingshifted and scaled versions of the mixed RF signal. The LO 420 controlthe transitions of the various switching mixers 440(0)-440(2 n) based onthe phase shifts. In one embodiment, there are (2n+1) switching mixertransitions in each LO period. For the case of n=0, the harmonic rejectmixer is substantially identical to the response of a single switchingmixer.

The harmonic mixer 400 includes a plurality of switching mixers, eachdriven by a distinct phase of an LO signal. This accomplishes the dualpurpose of permitting low-noise switching mixer designs driven byrelatively simple LO circuits, while achieving high harmonic rejectionacross a wide range of harmonics.

FIG. 5 is a simplified functional block diagram of an embodiment of aharmonic reject mixer 500 using three distinct phases. Thus, theembodiment of FIG. 5 corresponds to the generalized harmonic rejectmixer of FIG. 4 with n=1.

Thus, the RF input signal is coupled to three switching mixers410(0)-410(2). An output of a LO 420 is coupled to three distinct phaseshifters 430(0)-430(2). Using the formula provided above, the threephase shifters 430(0)-430(2) provide phase shifts of +45, 0, and −45degrees. The switching mixer 410(0)-410(2) outputs are coupled tocorresponding amplifiers 440(0)-440(2). The corresponding amplifiergains are scaled by (1/√{square root over (2)}), 1, and (1/√{square rootover (2)}), respectively. The outputs of the three amplifiers440(0)-440(2) are coupled to an input of a signal summer 450 where theyare summed to an output IF or baseband signal.

FIG. 6 is a simplified functional block diagram of a downconverter 600having harmonic reject mixers 620, 630, 640, and 650. Each of theharmonic mixers 620, 630, 640, and 650, can be configured as shown inFIG. 4 or 5.

The downconverter 600 of FIG. 6 is implemented as a double balancedquadrature mixer. The double balanced quadrature mixer configurationshown in FIG. 6 provides additional harmonic rejection of the 5th and9th harmonics. The additional harmonic rejection provided by the doublebalanced quadrature configuration permits the use of more simpleharmonic reject mixers 620, 630, 640, and 650 in the core. This may beadvantageous from a standpoint of fabrication, area, gate count,complexity, or cost.

In the downconverter 600 configured as a double balanced quadraturemixer, an input

RF signal is coupled to a polyphase filter 610. The polyphase filter 610generates multiple phase outputs from the input signal. In theembodiment shown in FIG. 6, the polyphase filter 610 is configured togenerate in-phase and quadrature signal outputs.

The quadrature signal outputs are coupled to first and second harmonicmixers 620 and 630. The in-phase signal outputs are coupled to third andfourth harmonic mixers 640 and 650.

The second and third harmonic mixers, 630 and 640, are driven with anin-phase LO signal. The first and fourth harmonic mixers, 620 and 650,are driven with a quadrature LO signal. The outputs of the first andthird harmonic mixers, 620 and 640, are combined to generate thequadrature downconverted signal, while the outputs of the second andthird harmonic mixers 630 and 650 are combined to generate the in-phasedownconverted signal.

Harmonic mixers, receivers using harmonic mixers, and methods ofprocessing input signals to reduce the contribution of input harmonicshave been described. A harmonic mixer can include a plurality ofswitching mixers, each driven with a distinct phase of a common LO. Theoutputs of the switching mixers can be combined or otherwise summed to asingle output signal. The output signal exhibits reduced contributionfrom input harmonics.

The steps of a method, process, or algorithm described in connectionwith the embodiments disclosed herein may be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. The various steps or acts in a method or processmay be performed in the order shown, or may be performed in anotherorder. Additionally, one or more process or method steps may be omittedor one or more process or method steps may be added to the methods andprocesses. An additional step, block, or action may be added in thebeginning, end, or intervening existing elements of the methods andprocesses.

The above description of the disclosed embodiments is provided to enableany person of ordinary skill in the art to make or use the disclosure.Various modifications to these embodiments will be readily apparent tothose of ordinary skill in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the disclosure. Thus, the disclosure is not intendedto be limited to the embodiments shown herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

1. A harmonic reject mixer comprising: a plurality of mixers, each mixerhaving a common radio frequency (RF) input; a generator operable togenerate a common local oscillation (LO) input signal; a phase shifterhaving an input coupled to receive the common LO input signal and beingoperable to generate a plurality of phase shifted output signals basedon the common LO input signal, the common LO input signal comprising aplurality of transitions during a period of each phase shifted outputsignal, wherein each of the plurality of phase shifted output signals isgenerated according to a respective transition of the plurality oftransitions of the common LO input signal, where each distincttransition in the plurality of transitions corresponds to a phase ofeach phase shifted output signal in the plurality of phase shiftedoutput signals and each of the phase shifted output signals is coupledto a LO input of a corresponding mixer of the plurality of mixers; and acombiner having a plurality of inputs, each input coupled to an outputof an associated mixer of the plurality of mixers, and configured toprovide a combined intermediate frequency (IF) output.
 2. The mixer ofclaim 1, wherein each of the plurality of mixers comprises a switchingmixer.
 3. The mixer of claim 1, wherein the phase shifter comprises aplurality of distinct phase shifters, each configured to provide adistinct predetermined phase shift.
 4. The mixer of claim 1, wherein thephase shifter is configured to generate a plurality of phase shiftedoutputs equally spaced about the span of −90 to +90 degrees.
 5. Themixer of claim 1, wherein: the plurality of mixers comprises threedistinct mixers; and the plurality of phase shifted outputs compriseoutputs shifted by −45, 0, and +45 degrees.
 6. The mixer of claim 1,further comprising a plurality of amplifiers, each of the plurality ofamplifiers coupled to a distinct one of the plurality of mixers andconfigured to amplify a mixer output by a gain based at least in part onan LO phase shift.
 7. The harmonic mixer of claim 6, wherein the gain isproportional to a sinusoidal function of the phase associated with theLO phase shift.
 8. The harmonic mixer of claim 1, wherein a differencebetween a frequency of the input and a frequency of the LO signal isgreater than a channel bandwidth.
 9. The harmonic mixer of claim 1,wherein the common LO input comprises a plurality of transitions overone LO period and each phase shifted output is generated according to adistinct transition in the plurality of transitions and each distincttransition in the plurality of transitions corresponds to the phase ofeach phase shifted output in the plurality of phase shifted outputs. 10.A method of harmonic rejection mixing, the method comprising: generatinga control signal; generating a plurality of distinct phased localoscillation (LO) signals based on the control signal, wherein thecontrol signal comprises a plurality of transitions during a period ofeach distinct phased LO signal, wherein each of the plurality ofdistinct phased LO signals is generated according to a respectivetransition of the plurality of transitions of the control signal, whereeach distinct transition in the plurality of transitions corresponds toone of the plurality of distinct phased LO signals; mixing an inputsignal with each of the plurality of distinct phased LO signals togenerate a plurality of mixed intermediate frequency (IF) outputsignals; and combining the plurality of mixed IF output signals toprovide an IF mixer output.
 11. The method of claim 10, wherein mixingthe input signal comprises: coupling the input signal to a plurality ofswitching mixers; and driving each of the plurality of switching mixerswith a distinct one of the plurality of phase of the LO signal.
 12. Themethod of claim 10, wherein generating the plurality of phases of the LOsignal comprises phase shifting the LO signal using a plurality ofdistinct phase shifters, each of the plurality of distinct phaseshifters providing a distinct phase shift.
 13. The method of claim 10,wherein generating the plurality of phases of the LO signal comprisesgenerating an odd number of distinct phases of the LO signal equallyspaced about a span of −90 to +90 degrees.
 14. The method of claim 10,wherein combining the plurality of mixed IF output signals comprisessumming the plurality of mixed IF output signals.
 15. The method ofclaim 10, further comprising amplifying each of the plurality of mixedIF output signals by a gain based on an LO phase shift.
 16. The methodof claim 10, wherein a difference between a frequency of the input and afrequency of the LO signal is greater than a channel bandwidth.
 17. Themethod of claim 15, wherein the gain is proportional to a sinusoidalfunction having a phase associated with the LO phase shift.
 18. Aharmonic reject mixer comprising: a control generator operable togenerate a control signal; an LO generator operable to generate aplurality of local oscillator (LO) signals based on the control signal,wherein the control signal comprises a plurality of transitions during aperiod of each distinct phased LO signal, wherein each of the pluralityof LO signals is generated according to a respective transition of theplurality of transitions of the control signal; a plurality of mixingcircuits operable to receive an input signal and the plurality of LOsignals having different phases, wherein each distinct transition in theplurality of transitions corresponds to the phase of each LO signal inthe plurality of LO signals, each of the mixing circuits being operableto receive a different one of the plurality of local oscillator signalsand being adapted to: generate a product of the input signal and thereceived local oscillator signal; and scale the product according to asinusoidal function having a phase associated with the received localoscillator signal; and an adder operable to combine a plurality ofoutputs from the plurality of mixing circuits.
 19. The harmonic mixer ofclaim 18, wherein the combined plurality of outputs corresponds to ademodulator input.
 20. The harmonic mixer of claim 18, wherein each ofthe plurality of mixing circuits comprises a switching mixer.
 21. Theharmonic mixer of claim 18, wherein the plurality of mixing circuits isan odd number of mixing circuits.
 22. The harmonic mixer of claim 18,wherein the input comprises a specified channel and a difference betweena frequency of the specified channel and a frequency of the LO signal isless than a bandwidth of the specified channel.
 23. The harmonic mixerof claim 22, wherein the adder output is baseband.
 24. The harmonicmixer of claim 22, wherein the adder output is substantially baseband.25. The harmonic mixer of claim 24, wherein the difference between thefrequency of the specified channel and the frequency of the LO signal isnon-zero.
 26. The harmonic mixer of claim 18, wherein the input is acommon RF signal.
 27. The harmonic mixer of claim 18, wherein the inputcomprises a specified channel and a difference between a frequency ofthe specified channel and a frequency of the LO signal is greater than abandwidth of the specified channel.
 28. The harmonic mixer of claim 27,wherein the adder output is an IF output.
 29. The harmonic mixer ofclaim 18, wherein the number of distinct transitions in the plurality oftransitions is equal to a number of mixing circuits in the plurality ofmixing circuits.